1. Field of the Invention
The present invention relates to heat transfer tube for a heat exchanger used for a room air conditioner or the like, and more particularly to a heat transfer tube with grooves in an inner surface thereof which has a high performance as an evaporator and a condenser.
2. Related Art
In the past, a heat transfer tube used for a heat exchanger is used as an evaporator and a condenser. That is, within a heat transfer tube, a refrigerant liquid is evaporated or refrigerant gas is condensed to thereby perform a heat exchanging. A conventional heat transfer tube formed with a plurality of kinds of groups of grooves in an inner surface of a metal tube is disclosed in Japanese Patent Application Laid-Open Nos. Hei 3-13796 and 4-158193 Publications.
In the heat transfer tube disclosed in Japanese Patent Application Laid-Open Nos. Hei 3-13796, a group of helical grooves are formed so as to divide a circumference of an inner surface of the tube into more than four even numbers, and these groups of helical grooves are formed so that torsional angles with respect to a direction of tube axis are mutually reversed between portions adjacent to each other. In this heat transfer tube, since there is no reverse point in an inclining direction of a groove of grooves caused by hair pin processing, it is possible to prevent the heat transfer performance in groove portions subjected to hair pin processing from being lowered. Further, by the liquid collecting action of condensed liquid at the time of condensation, a liquid film thickness in the tube is standardized so that disengagement of liquid from a groove joining portion is promoted, thus improving the condensation performance. Further, since in the inner surface of the heat transfer tube, a group of helical grooves are formed at a fixed groove pitch in a direction of tube axis, and a flat portion is provided in suitably spaced apart between the helical grooves along the tube axis, the hair pin bending processability can be improved.
In the heat transfer tube disclosed in Japanese Patent Application Laid-Open Nos. Hei 4-158193, a plurality of kinds of concavo-convex groups in a fixed spaced apart relation. The concavo-convex group comprises concave portions and groove portions, which are arranged in parallel alternately. A single concavo-convex group and concavo-convex groups adjacent to the first mentioned concavo-convex group are formed to be different in at least one or more elements out of a pitch of groove, a dimension of groove, a shape of groove and a groove direction with respect to a tube axis. Therefore, a flow of refrigerant in the tube becomes stirred up to improve the heat transfer performance. When three or more concavo-convex groups are provided, the heat transfer performance can be further improved.
On the other hand, a heat transfer tube in which a group of helical grooves and projections parallel with a tube axis direction crossing with the group of helical grooves are provided in the inner surface of a metal tube is disclosed in Japanese Patent Publication Nos. Hei 5-71874 and 6-10594 Publications. In the heat transfer tube disclosed in Japanese Patent Publication No. Hei 5-71874, the group of helical grooves is formed with the same torsional angle with respect to the tube-axis direction, and in Japanese Patent Publication No. Hei 6-10594, the groups of helical grooves formed on both sides of the projections are formed symmetrically with the projections. These heat transfer tubes are provided in the inner surface with a group of helical grooves and one or more projections parallel with the tube axis direction crossing with the group of helical grooves. A flow of refrigerant liquid within the grooves is cut off by the projection(s) to disappear a liquid film whereby the heat transfer performance can be improved. Further, since the projection parallel with the tube-axis direction is formed, a flow of refrigerant liquid in the tube-axis direction is smooth, and a pressure loss with respect to the tube-axis direction can be reduced.
However, the aforementioned conventional heat transfer tubes have the following problems. First, in the heat transfer tube disclosed in Japanese Patent Application Laid-Open No. 3-13796 Publication, the plurality of kinds of groups of helical grooves are provided, which are formed so that the torsional angles are the same and mutually reversed with respect to the tube-axis direction between portions adjacent to each other. Because of this, the refrigerant liquid in one group of grooves is impaired in flow by the other group of grooves having a reversed torsional angle. Therefore, in an evaporator in which a refrigerant liquid is supplied, which refrigerant liquid is evaporated for heat exchange, a refrigerant is not uniformly spread over the entire inner wall of the tube, lowering the evaporation performance.
In the heat transfer tube disclosed in Japanese Patent Application Laid-Open Nos. Hei 4-158193, a plurality of kinds of groups of helical grooves, which are formed to be different in at least one or more elements out of a pitch of groove with respect to the tube-axis direction between portions adjacent to each other, a dimension of groove, a shape of groove, and a torsional angle of the group of grooves with respect to the tube-axis direction. Therefore, in the conventional heat transfer tube, a flow of refrigerant is not impaired but at the time of evaporation, a pressure loss cannot be sufficiently reduced so that the evaporation performance lowers and at the time of condensation, a discharge property of condensed liquid is not enough so that a contact property between the heat transfer surface and the refrigerant gas lowers to lower the condensation performance. Further, when the group of helical grooves having the same torsional angle with respect to the tube-axis direction is provided over the entire inner surface of the tube, the condensed liquid tends to spread over the entire heat transfer surface at the time of condensation so that the heat transfer surface is covered with the condensed liquid to lower the condensation performance.
In the heat transfer tube disclosed in Japanese Patent Laid-Open No. Hei 5-71874 Publication, a plurality of groups of grooves are formed in the same direction in the entire inner surface of the tube. Therefore, the condensed liquid tends to spread over the entire heat transfer surface at the time of condensation so that even if the condensed liquid is discharged by the projections, the heat transfer surface is covered with the condensed liquid, thus lowering the condensation performance.
In the heat transfer tube disclosed in Japanese Patent Laid-Open No. Hei 6-10594 Publication, two kinds of groups of grooves are formed symmetrically between portions adjacent to each other with respect to the projections. Therefore, a flow of refrigerant liquid by one group of grooves generated at the time of evaporation becomes impaired by the other group of grooves, and when the flow of refrigerant liquid within the grooves is cut off by the projections, the refrigerant liquid is not spread over the entire heat transfer surface, thus lowering the evaporation performance.
The present invention has been achieved in view of the aforementioned problems. It is an object of the present invention to provide a heat transfer tube with grooves in an inner surface thereof for heat exchange with a refrigerant flowing through the tube, in which shapes of two kinds of group of grooves formed in the inner surface of the tube are adequately set, a plurality of sets of two kinds of groove processing regions having these groups of grooves are arranged, and a linear groove region extending in a direction of a tube-axis is arranged between the groove processing regions to thereby provide excellent evaporation performance and condensation performance.